1. Field of the Invention
This invention relates generally to gaskets and more particularly to improved gaskets for use in gasoline and diesel engines, compressors, oil coolers, and other machinery.
2. Description of the Related Art
Gaskets have long been used to seal interfaces between components in a wide variety of machines and especially in gasoline and diesel engines. Many types and forms of gaskets have been adopted including compressible fibrous gaskets, controlled compression rubber gaskets, metal gaskets, layered or composite gaskets, cork gaskets, rubber gaskets, and others. A detailed description of the background of some of these types of gaskets and of much of the art related to the present invention is included in our pending U.S. Utility Patent Application entitled xe2x80x9cEdge Coated Gaskets and Method of Making Same.xe2x80x9d For purposes of brevity in this specification, including the claims, is hereby incorporated by reference as if fully set forth herein.
As discussed in detail in the attached application, providing a polymer coating on the interior edge of a compressible base sheet of gasket material results in an edge coated gasket with significantly enhanced sealability. When the edge coating on such gaskets is formed with protruding rims or with face coatings, the gasket can provide excellent sealability even under adverse conditions where traditional gaskets tend to fail. These conditions include rough or damaged flange surfaces, warped flanges, thin flanges that tend to deflect when clamped together, and poor bolt placement that can result in regions of substantially reduced compression stress. Further, the combination of an appropriately profiled polymer edge coating on a compressible base sheet results in a complex sealing mechanism that provides excellent sealability while simultaneously preserving the desirable property of compression failure resistance inherent in compressible gasket sheet materials.
As further discussed in the incorporated disclosure, edge coated compressible gaskets also address successfully the problem of stress relaxation failure, which is the failure mode most common in controlled compression rubber gaskets. Stress relaxation failure occurs when the rubber or polymer beads of controlled compression rubber gaskets relax over time due, for example, to rearrangement of polymer molecule chains in response to the stress state, shrinkage of the bead as a result of molecular chain cross-linking, softening and swelling of the bead due to fluid penetration, a degradation of the polymer molecule chains due to heat, fluid, and oxygen exposure. Since the flange gap is limited by a rigid carrier or compression limiters in controlled compression gaskets, the above enumerated conditions result in a reduction of the surface stress between the rubber beads and the flange surfaces. When the surface stress falls below the threshold required to prevent interfacial leakage, the seal is lost. An edge coating on a compressible base sheet is much less subject to stress relaxation failure because the base sheet itself relaxes a bit over time, progressively reducing the flange gap. This offsets any stress relaxation in the edge coating material and the integrity of the seal is maintained.
It has been found that the tackiness or surface adhesion inherent in many types of polymer edge coating materials enhances the sealability and further reduces the detrimental effects of stress relaxation in edge coated gaskets. Even in cases where stress between the edge coating and a flange surface may fall below the sealing threshold for whatever reason, the adhesion of the edge coating material to the flange surface maintains the seal and prevents failure of the gasket.
Unfortunately, the rubber materials from which the beads of controlled compression rubber gaskets are formed are substantially dry and exhibit very little surface adhesion. Thus, these types of gaskets have not benefited from the added reliability provided by the surface adhesion phenomenon. Further, in the case of some, but not all, polymer edge coatings, it is very difficult to tailor the polymer material to have the proper spring rate and other physical properties required by a particular application and also to exhibit a desired surface adhesion for the application. To some extent, these can be competing properties in that measures taken to enhance one tend to degrade the other and vice versa.
Thus, there exists a need for edge coated gaskets in which a predetermined surface adhesion between the coating material and the flange surfaces can be established to enhance sealability. A further need exists for a controlled compression rubber gasket wherein the rubber bead of the gasket can benefit from the advantages of surface adhesion. An efficient and reliable method of fabricating such gaskets is also needed. It is to the provision of such gaskets and such a method that the present invention is primarily directed.
Briefly described, the present invention, in preferred embodiments thereof, comprises edge coated and controlled compression rubber gaskets in which the edge coatings and rubber beads are provided with predetermined and specifically tailored surface adhesion properties appropriate to particular application requirements. In one and perhaps the simplest embodiment, the polymer material from which an edge coating is formed on and edge of a compressible base sheet is formulated to exhibit both the appropriate physical characteristics and the appropriate surface adhesion properties required for a specific application. In situations where both of these properties cannot be established simultaneously in a single polymer or homogeneous polymer blend, the invention contemplates an edge coating wherein a core of polymer material with the appropriate physical properties is covered or overcoated with a layer of polymer having the proper surface adhesion characteristics. In this instance, a layered or stratified edge coating is formed.
To provide traditional controlled compression rubber gaskets with the advantages of surface adhesion, the invention contemplates coating the rubber beads of such gaskets with a relatively thin layer of polymer or other appropriate material having the desired surface adhesion properties. In this way, if the bead suffers catastrophic stress relaxation failure, a seal can nevertheless be maintained by the surface adhesion provided by the coating. The method of this invention in one embodiment includes selecting a polymer edge coating material having predetermined physical and surface adhesion properties and forming an edge coating from the selected material on an edge of a gasket base sheet. The method also includes selecting a first edge coating material with predetermined physical properties, selecting a second edge coating material with predetermined surface adhesion properties, forming an edge coating on a gasket base sheet from the first coating material, and depositing a layer of the second edge coating material on the edge coating. The result is a layered edge coated gasket with tailored physical properties and tailored surface adhesion. Finally, the method of the invention also contemplates depositing a layer of material having selected surface adhesion properties onto the rubber bead or beads of a controlled compression rubber or other rubber edged gasket to provide the advantageous benefits of surface adhesion to such gaskets.
Thus, enhanced edge coated, controlled compression rubber, and rubber edged gaskets are now provided that address the problems of prior art gaskets and that provide enhanced seals through adhesion to flange surfaces between which they are clamped.
Accordingly, in one aspect, the invention relates to a gasket for creating a seal between a pair of surfaces, where the gasket comprises a base sheet having an adhesive element as an edge coating on at least one edge, the adhesive element being adapted to bond with the surfaces to enhance the seal provided by the gasket.
In another aspect, the invention relates to a gasket for creating a seal between a pair of surfaces, where the gasket comprises a non-compressible carrier as a base sheet having at least one edge forming a boundary of a gasket aperture and having at least one face comprising a recess; and at least one adhesive element as a bead structure disposed in the recess, the adhesive element being adapted to bond with the surfaces to enhance the seal provided by the gasket.
In yet another aspect, the invention relates to a gasket for creating a seal between a pair of flange surfaces, where the gasket comprises a non-compressible core having an interior edge; a coating of material which is at least partially compressible; and an adhesive element applied on at least one face of the gasket in an area adjacent to the interior edge of the non-compressible core.
In still another aspect, the invention relates to a gasket for creating a seal between a pair of flange surfaces, where the gasket comprises an o-ring having an adhesive element